1. Field of the Invention
The present invention relates to the structure of a metal mold used to produce a molded article by injecting melted resin into a cavity of predetermined shape, and a display apparatus having a front cabinet molded with such a metal mold.
2. Description of the Prior Art
FIGS. 5 and 6 show cross-sectional views of a metal mold 10. The metal mold 10 is used to mold the front cabinet of a television, and consists of a male mold 20 and a female mold 30. As shown in (1) of FIG. 5, a convex portion 21 is formed at around the center of the surface of the male mold 20 facing the female mold, and a concave portion 31 is formed on the surface of the female mold 30 facing the male mold, in which the convex portion of the male mold 20 can be accommodated. In this construction, as shown in (2) of FIG. 5, when the male mold 20 and the female mold 30 are approximated to each other, and the top surface 21a of the convex portion 21 and the bottom surface 31a of the concave portion 31 are made to contact, the surfaces 22 and 32 will face each other with a predetermined space kept between them, and the sides 21b of the convex portion 21 and the sides 31b of the concave portion will also face each other with a predetermined space kept between them.
By filling in the space between the male mold 20 and female mold 30 formed in this way with melted hot resin and then cooling it down to a predetermined temperature, a front cabinet 40 with the cross section as shown in (1) of FIG. 5 was produced. The cross section of the front cabinet shown in this figure corresponds to the cross section taken on B-B line in FIG. 1. The produced front cabinet 40 houses a display apparatus 50 such as an LCD panel.
In addition, related technologies are also known, such as: a manufacturing method in which plastic molded articles are molded without expanding their outer dimensions and without damaging their textured shapes (Japanese Patent Laid-open Publication No. 1995-308945); a method in which a convex portion is provided at the boundary between the metal mold and film gate (Japanese Patent Laid-open Publication No. 1996-132481); and a technology in which a continuous thick-walled portion is formed around the outer peripheral of a front cabinet to increase its strength (Japanese Patent Laid-open Publication No. 1996-142230).
In the above metal mold 10, it will be seen from FIG. 2 that the convex portion 21 of the male mold 20 forms, at the front side of the front cabinet 40, an opening 42 for exposing outward a display surface 51 of the display apparatus 50 within the front cabinet. Accordingly, one end (a panel touching end 43a) of an inward bent portion 43, which is formed so as to surround the opening 42 from the front edge portion 41 of the front cabinet 40, roughly contacts the display surface 51.
In such a construction, if different types of displays from different manufactures are employed as the display apparatus 50, the display surface 51 may not be always positioned at the same location, and consequently the distance between the display surface 51 and the front of the front cabinet 40 may vary depending on the type of the display apparatus 50. In this case, if there occurs a more than allowable clearance (e.g., 0.2 mm) between the display surface 51 and the panel touching end 43a, that television will be rejected as a defective in the product inspection. Therefore, conventionally, the clearance between the display surface 51 and the panel touching end 43a has been eliminated by modifying the metal mold 10 as described below, to adjust the length of a boss 44 and/or the inward bent portion 43 regardless of types of the display 50.
The case of adjusting the length of the boss 44 is described here. The boss 44 is formed at a plurality position on the inside of the front cabinet 40, projecting toward the rear of the television, and typically is secured with a screw or the like to a corresponding boss or screw hole provided on the rear cabinet. This allows the length of the front of the front cabinet 40 and the display surface 51 to be adjusted by adjusting the length of each boss.
However, to lengthen each boss in this adjustment, it is necessary to drill a plurality of boss molding holes 33 of exactly the same depth, and to shorten each boss 44 it is necessary to fill in (i.e., shallow) the boss molding holes to exactly the same extent. This means that the conventional method of adjusting the length of each boss 44 requires a lot of works or difficult problems when modifying a metal mold. Furthermore, although it is necessary to fill in the boss molding hole 33 by welding with a metal, the portion around the boss molding hole 33 is often made of a material with higher heat conductivity than any other portion of a metal mold, to increase the cooling efficiency. Therefore, the boss molding hole 33 was not a portion that is suitable for adding a metal material by means of welding, because of a possible decrease in the strength of the metal mold or the like.
Next, adjusting the length of the inward-bent portion 43 for employing the metal mold 10 is described. In making the adjustment, a metal mold member P of predetermined thickness t was welded to the top 21a of the convex portion 21 as shown in FIG. 6, and the bottom 31a of the concave portion was shaved off by the thickness t (the level of the bottom 31a before being shaved off is shown by a dotted line, and the level of that after being shaved off is shown by a solid line). That is, the depth of the concave portion 31 is set in advance to a distance at which the display surface 51 of the display apparatus 50 is expected to be closest to the front of the front cabinet 40, and if the length of the inward-bent portion 43 is required, a member of the thickness equal to that length was added to the convex portion 21 and also the concave portion 31 was shaved off by the depth equal to that length.
In other words, the conventional art requires both the welding and shaving works, thus requiring many steps for modifying a metal mold. Moreover, it is difficult to add a member of precise depth to the convex portion 21 and shave off the concave portion by the same depth, often resulting in errors. Because of this, this art is a rather difficult technique of adjusting the length of the inward-bent portion 43, which requires a one-tenth of mm order precision. Furthermore, undesired molded portions called flash may result from the errors around the inward-bent portion 43, thus lowering the quality of the front cabinet 40.